新增章 [Cookbook - 时间计算和转换]

src/SUMMARY.md

@@ -184,6 +184,15 @@
   - [数据库]()
     - [SQLite](cookbook/database/sqlite.md)
     - [Postgres](cookbook/database/postgres.md)
+  - [日期和时间]()
+    - [时间计算和转换](cookbook/datetime/duration.md)
+    - [解析和显示](cookbook/datetime/parsing.md)
+  - [开发者工具]()
+    - [日志](cookbook/devtools/log.md)
+    - [配置日志](cookbook/devtools/config-log.md)
+    - [版本](cookbook/devtools/version.md)
+    - [构建时工具](cookbook/devtools/build-tools.md)
+
 
 - [Rust 最佳实践](practice/intro.md)
   - [对抗编译检查](practice/fight-with-compiler/intro.md)

src/cookbook/datetime/duration.md

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+# 时间计算和转换
+
+### 测量某段代码的耗时
+测量从 [time::Instant::now](https://doc.rust-lang.org/std/time/struct.Instant.html#method.now) 开始所经过的时间 [time::Instant::elapsed](https://doc.rust-lang.org/std/time/struct.Instant.html#method.elapsed).
+
+```rust,editable
+use std::time::{Duration, Instant};
+
+fn main() {
+    let start = Instant::now();
+    expensive_function();
+    let duration = start.elapsed();
+
+    println!("Time elapsed in expensive_function() is: {:?}", duration);
+}
+```
+
+### 对日期和时间进行计算
+使用 [DateTime::checked_add_signed](https://docs.rs/chrono/*/chrono/struct.Date.html#method.checked_add_signed) 计算和显示从现在开始两周后的日期和时间，然后再计算一天前的日期 [DateTime::checked_sub_signed](https://docs.rs/chrono/*/chrono/struct.Date.html#method.checked_sub_signed)。
+
+[DateTime::format](https://docs.rs/chrono/*/chrono/struct.DateTime.html#method.format) 所支持的转义序列可以在 [chrono::format::strftime](https://docs.rs/chrono/*/chrono/format/strftime/index.html) 找到.
+
+```rust,editable
+use chrono::{DateTime, Duration, Utc};
+
+fn day_earlier(date_time: DateTime<Utc>) -> Option<DateTime<Utc>> {
+    date_time.checked_sub_signed(Duration::days(1))
+}
+
+fn main() {
+    let now = Utc::now();
+    println!("{}", now);
+
+    let almost_three_weeks_from_now = now.checked_add_signed(Duration::weeks(2))
+            .and_then(|in_2weeks| in_2weeks.checked_add_signed(Duration::weeks(1)))
+            .and_then(day_earlier);
+
+    match almost_three_weeks_from_now {
+        Some(x) => println!("{}", x),
+        None => eprintln!("Almost three weeks from now overflows!"),
+    }
+
+    match now.checked_add_signed(Duration::max_value()) {
+        Some(x) => println!("{}", x),
+        None => eprintln!("We can't use chrono to tell the time for the Solar System to complete more than one full orbit around the galactic center."),
+    }
+}
+```
+
+### 将本地时间转换成其它时区
+使用 [offset::Local::now](https://docs.rs/chrono/*/chrono/offset/struct.Local.html#method.now) 获取本地时间并进行显示，接着，使用 [DateTime::from_utc](https://docs.rs/chrono/*/chrono/struct.DateTime.html#method.from_utc) 将它转换成 UTC 标准时间。最后，再使用 [offset::FixedOffset](https://docs.rs/chrono/*/chrono/offset/struct.FixedOffset.html) 将 UTC 时间转换成 UTC+8 和 UTC-2 的时间。
+
+```rust,editable
+use chrono::{DateTime, FixedOffset, Local, Utc};
+
+fn main() {
+    let local_time = Local::now();
+    let utc_time = DateTime::<Utc>::from_utc(local_time.naive_utc(), Utc);
+    let china_timezone = FixedOffset::east(8 * 3600);
+    let rio_timezone = FixedOffset::west(2 * 3600);
+    println!("Local time now is {}", local_time);
+    println!("UTC time now is {}", utc_time);
+    println!(
+        "Time in Hong Kong now is {}",
+        utc_time.with_timezone(&china_timezone)
+    );
+    println!("Time in Rio de Janeiro now is {}", utc_time.with_timezone(&rio_timezone));
+}
+```

src/cookbook/datetime/parsing.md

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+# 解析和显示

src/cookbook/devtools/build-tools.md

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+# 构建时工具

src/cookbook/devtools/config-log.md

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+# 配置日志

src/cookbook/devtools/log.md

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+# 日志

src/cookbook/devtools/version.md

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+# 版本